Ultrasonic transmission devices are well known for use in a variety of applications, such as surgical operations and procedures. In a typical ultrasonic transmission device, a generator sends electrical energy to a transducer. The transducer converts the electrical energy into vibrational motion at ultrasonic frequencies. The vibrational motion is transmitted to the distal end of an acoustical assembly of the transmission device.
The acoustical assembly, when tuned to the frequency of the generator, maintains a standing wave therethrough. The standing wave causes the acoustical assembly to expand and contract in a continuous manner. However, as the ultrasonic energy is transmitted through the acoustical assembly, unwanted transverse motion may reduce axial (i.e. forward and backward) motion of the distal end of the acoustical assembly and may produce fatigue in the assembly. In addition, the transmission of the ultrasonic energy through the acoustical assembly can generate undesirable heat which, if not controlled, could damage the ultrasonic transmission device or prevent optimal performance of the device.
Isolation mounts, such as O-rings, may be mounted around the periphery of the acoustic assembly at positions of minimal axial ultrasonic activity (i.e. nodes) to dissipate or dampen the unwanted ultrasonic energy transmitted through the assembly. For example, U.S. Pat. Nos. 5,346,502 and 5,322,055, which are herein incorporated by reference, disclose ultrasonic instruments each including a working member having a shaft and a blade. The shaft of each working member has a plurality of silicone rings disposed near nodes of the shaft to isolate the shaft from a sheath and to dampen undesired vibration. However, these silicone rings tend to dissipate too much desirable resonance ultrasonic energy and may not eliminate unwanted vibrations. In addition, waste heat may be generated in various locations along the shaft which may heat the surface of the sheath.
Conventional ultrasonic devices may also dampen unwanted vibration by the use of a water layer between a transmission component and a sheath. For example, U.S. Pat. No. 5,248,296 discloses an ultrasonic device having sheath that surrounds a wire. A small annular space or passageway is formed between the sheath and the wire. The passageway is filled with a pressurized fluid, such as water or saline solution. Although the fluid may effectively dampen unwanted vibrations of the wire, the fluid usually tends to cause dissipation of desired longitudinal vibration. In addition, because the fluid increases in temperature, the fluid has to be circulated or discharged in order to remove the heat. Furthermore, the use of fluids in certain ultrasonic devices may be inconvenient or impractical.
Accordingly, there is a need for an improved apparatus to dampen unwanted vibration of a transmission component. It would be beneficial to allow the desired ultrasonic energy to propagate to the distal end of the transmission component while dissipating unwanted vibrational energy without the use of a fluid. It would also be desirable to provide a damping apparatus that was simple and inexpensive to manufacture.